[GRASSLIST:3334] Re: Correcting SRTM with MrSID images

[Bryan K. Wright]

Hi folks,

tatel at euskalnet.net said:
> Unfortunatelly I can't register SRTM and image data. After
> reprojecting image from UTM-WGS84 to Lat_Lon-WGS84, it seems to be a
> shift of about 250-300 meters towards W in SRTM from image. More
> confusingly, this 

	I've also seen a shift of about 200 meters between MrSid-format
DOQQs and the corresponding USGS DRG files.  The MrSid files were decoded
using the Windows version of mrsiddecode, which produces a tiff and a
tfw file.  There were actually two oddities in the tfw files.  Here's
a quote from an earlier message I posted to the list about this problem:

bryan at ayesha.phys.Virginia.EDU said:
> 	Two oddities with the tfw files, though:  the fourth line of the file
> (cell size) ended up being a positive number, which r.in.tiff  didn't
> like.  Adding a minus sign fixed the problem.  I also found that the
> last line of the file (northing) was offset by 200 meters relative to
> the USGS topo maps I'm using.  These may just be problems with the
> original sid/sdw files I happened to be using. 

	Since then I've heard from a couple of other people who've
noticed the same thing.

						Bryan
-- 
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Bryan Wright                |"If you take cranberries and stew them like 
Physics Department          | applesauce, they taste much more like prunes 
University of Virginia      | than rhubarb does."  --  Groucho 
Charlottesville, VA  22901  |			
(434) 924-7218              |         bryan at virginia.edu
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